After this lesson, your students should be able to ·classify chemical and physical changes ·describe how heating can cause physical/chemical changes to matter
Points to note while teaching:
·Highlight to students that although most physical changes are observable, not all chemical changes are observable. Physical and chemical changes may sometimes occur simultaneously in a reaction. Misconception: Solutes dissolving in a solvent does not indicate a chemical reaction.
Lesson component
Content
Resources required
Time Frame
Starters/Triggers
Simple experiment 1 Conduct a simple experiment in which phenolphthalein is added to a beaker of alkali e.g. sodium hydroxide. Both solutions are colourless but upon addition, a pink coloration is observed. (The concept that phenolphthalein will change from colourless to pink in the presence of an alkali would have been explored in the chapter of ‘Acids, Bases and Salt’.)
Questions to ask:
1. Why do two colourless mixtures mixed together produce a pink solution?
2. Is the change a result of physical or chemical reaction?
3. What defines a physical or chemical reaction?
Simple experiment 2 Cut an apple into two sections. Let students observe the exposed area. After ten minutes, let students observe the change that has taken place to the inner part of the apple.
Questions to ask:
1. What has caused the colour change in the apple?
2. Is the change a result of physical or chemical reaction?
The oxygen in the air has reacted chemically with the apple and caused a colour change.
Phenolpthalein
sodium hydroxide
beaker
Apple
15 mins
Concept Development
Pupils to carry out the practical activities from practical workbook
Activities
Activity 1 : Heating Copper (II) Carbonate
Activity 2: Heating of Magnesium
Activity 3: Heating of Sodium Chloride
Activity 4: Heating of Wax
Procedures
1. Ask students to collect pre-packed samples, test tube, test tube holder, goggles, bunsen burner and lighter.
2. Students are reminded about safety when heating substances.
3. Students to note the colour of substance before heating and after heating.
4. Students to answer questions in the practical book.
5. Ask students to explain their observations.
i. What caused the change in colour?
ii Can the original substance be obtained again?
iii. Explain why you would classify this as a physical or chemical change.
PowerPoint slides
Practical Workbook
40 mins
Review Questions/ Conclusion
Allow students to attempt the questions on their own in the discussion page.
1. Define physical and chemical changes.
2. Discuss some examples of physical changes and point out the reasons why they are classified as physical changes.
3. Discuss some examples of chemical changes and point out the reasons why they are classified as chemical changes.
Changing Matter
Section 1: Observing Changes
Section 2: Types of Changes
Level: Sec 2E/NA
Duration: 2 periods (70 mins)
Learning Outcomes
After this lesson, your students should be able to· classify chemical and physical changes
· describe how heating can cause physical/chemical changes to matter
Points to note while teaching:
· Highlight to students that although most physical changes are observable, not all chemical changes are observable. Physical and chemical changes may sometimes occur simultaneously in a reaction. Misconception: Solutes dissolving in a solvent does not indicate a chemical reaction.Resources required
Conduct a simple experiment in which phenolphthalein is added to a beaker of alkali e.g. sodium hydroxide. Both solutions are colourless but upon addition, a pink coloration is observed. (The concept that phenolphthalein will change from colourless to pink in the presence of an alkali would have been explored in the chapter of ‘Acids, Bases and Salt’.)
Questions to ask:
1. Why do two colourless mixtures mixed together produce a pink solution?
2. Is the change a result of physical or chemical reaction?
3. What defines a physical or chemical reaction?
Simple experiment 2
Cut an apple into two sections. Let students observe the exposed area. After ten minutes, let students observe the change that has taken place to the inner part of the apple.
Questions to ask:
1. What has caused the colour change in the apple?
2. Is the change a result of physical or chemical reaction?
The oxygen in the air has reacted chemically with the apple and caused a colour change.
Activities
Activity 1 : Heating Copper (II) Carbonate
Activity 2: Heating of Magnesium
Activity 3: Heating of Sodium Chloride
Activity 4: Heating of Wax
Procedures
1. Ask students to collect pre-packed samples, test tube, test tube holder, goggles, bunsen burner and lighter.
2. Students are reminded about safety when heating substances.
3. Students to note the colour of substance before heating and after heating.
4. Students to answer questions in the practical book.
5. Ask students to explain their observations.
i. What caused the change in colour?
ii Can the original substance be obtained again?
iii. Explain why you would classify this as a physical or chemical change.
1. Define physical and chemical changes.
2. Discuss some examples of physical changes and point out the reasons why they are classified as physical changes.
3. Discuss some examples of chemical changes and point out the reasons why they are classified as chemical changes.
§ __http://www.bbc.co.uk/schools/ks2bitesize/science/revision_bites/reversible_irreversible1.shtml__
§ Further reading on irreversible and reversible changes with introduction to the effect of heating, mixing and burning substances causing irreversible changes.
§ Clear misconception that dissolving solutes are not an indication of a chemical reaction.